Three series of investigations are proposed. The first involves a comprehensive anatomical and physiological examination of the serotonergic raphe-SPN pathway. Using autoradiography, horseradish peroxidase (HRP), lesion, microstimulation, and extracellular recording techniques, studies have been designed to: (a) localize the cells of origin and spinal trajectory of the raphe-SPN system; (b) establish the conduction velocities and degree of convergence and divergence of raphe axons terminating upon the SPNs; (c) investigate the spatial and temporal properties of the inhibition of SPN discharge associated with activation of this descending system; (d) assess the involvement of the raphe in baroreceptor and somatosympathetic reflexes; and (e) establish the role of the raphe in the "tonic" and "phasic" modulation of arterial blood pressure. The second involves anterograde transport studies to localize the cells of origin of the catecholaminergic input(s) upon the SPNs. Using autoradiography, the spinal projections of cells in the ventrolateral medullary region, locus coeruleus, and subcoeruleus would be described. Anterograde tract tracing would also be initiated on the paraventricular nucleus of the hypothalamus. The final project involves a preliminary electron microscopic description of the cytological characteristics of axon terminals on HRP-labelled preganglionic neurons.